I've just finished preparing a detailed guide concerning creating
accomplishments, which aims to be useful for Accomplishments
Contributors and third-party developers.
I consider it complete. You can find it at
https://wiki.ubuntu.com/Accomplishments/CreatingGuide.

I hope I have not missed anything. Please share your thoughts, and
feel free to edit & improve it.

This is very cool :-)

One whiny thing: accomplishments don't necessarily *need* a script.
There are really three sorts of accomplishments[1]:

* ones awarded when you do something not on your computer, such as
Launchpad bug-filing (these obviously need a script to talk to Launchpad
and see if you've accomplished the task)
* ones awarded for doing something on your computer (such as beating
Minesweeper) but which are checked for completeness by a script rather
than by the application itself (which need the script, of course)
* ones awarded for doing something on your computer (such as beating
Minesweeper) which are awarded by the application itself

The third sort don't need a script; Minesweeper should, ideally, award
you accomplishments itself rather than having a separate thing in the
scriptrunner award them. Of course, there aren't any apps which do this
yet, and so the separate-script technique is being used, but in a
perfect world we wouldn't use separate scripts to do things that the
application should be doing for itself. Do we want to encourage people
to write loads of separate scripts, or should we be trying to get apps
themselves to support the Accomplishments system?